Hitherto, as liquid-crystal display devices using a transmission-type liquid-crystal panel, liquid-crystal display devices in which a plurality of backlights are used to change the amount of light that is made to enter each of display areas (blocks) on a liquid-crystal panel and expansion of a dynamic range of the luminance of an image to be displayed is realized have been proposed (see, for example, Patent Document 1).
As described above, in a case where each of a plurality of backlights causes light to enter a corresponding one of display areas corresponding to a liquid-crystal panel, as shown in FIG. 1, the amount of light to be emitted by each backlight is obtained from an image signal of an image to be displayed.
That is, in FIG. 1, an image signal of a step-shaped waveform, indicated by an arrow All, is input to a light-emission amount computation unit 11 and a dividing unit 12. On the basis of the image signal, the light-emission amount computation unit 11 computes the amount of light to be emitted from one backlight 13. Furthermore, the dividing unit 12 divides the supplied image signal by the amount of light from the light-emission amount computation unit 11, thereby calculating the transmittance of light in the display area of a liquid-crystal panel 14 corresponding to the backlight 13. Meanwhile, in the waveform of FIG. 1, the horizontal axis indicates the horizontal position of a backlight, and the center position indicates the center position of the backlight 13.
Here, the size of one backlight 13 is larger than the size of the pixel of the display area of the liquid-crystal panel 14. Therefore, the amount of light of the backlight 13 is computed on the basis of the pixel value of each pixel of an image displayed on the display area of the liquid-crystal panel 14 corresponding to the backlight 13.
Then, when the amount of light is computed, the backlight 13 emits light on the basis of the amount of light calculated by the light-emission amount computation unit 11, and causes light to enter the liquid-crystal panel 14. As a result, light of a waveform indicated by an arrow A12 is emitted from the backlight 13. That is, since light from the backlight 13 is diffused, the amount of light in the center of the light is largest, and the amount of light decreases with increasing distance from the center.
Furthermore, the liquid-crystal panel 14 allows light from the backlight 13 to be transmitted therethrough at a waveform indicated by an arrow A13, that is, at a transmittance computed by the dividing unit 12. As a result, in the display area of the liquid-crystal panel 14, as indicated by an arrow A14, an image that is nearly the same as the image of the input image signal is displayed.
As described above, the light-emission level of each backlight is determined on the basis of the input image signal.
However, when the light-emission level is computed on the basis of the information of the input image signal of each of blocks directly above, which are simply divided as described above, the input image signal does not have intra-block position information, and diffusion at the time when the block emits light is not considered. As a consequence, in a case where the level of the diffused light is low, pixels having insufficient luminance appear.
However, if the light-emission level is increased to prevent such luminance insufficiency, the block emits light needlessly, with the result that the original advantages, such as reduction of consumption of power and improvement of the black level, are sacrificed.
Furthermore, at the actual light-emission time, since light is diffused outside the divided areas, calculations in which an influence of light emission of the other blocks is considered become necessary. In a case where the value of the backlight is to be computed from only the included input image signal directly above, since the state of the other blocks is ignored, the block emits light needlessly. A method of controlling the amount of light emission using the histogram and the average value of the entire frames has been considered, but optimization of the amount of light emission for each local block cannot be performed.
Therefore, a technology has been proposed in which light-emission levels of other blocks are considered and adjusted, simultaneous equations of the order in an amount corresponding to the number of divisions are solved to compute and adjust the light-emission level of each block (see, for example, Patent Document 2).
Related Art Documents
Patent Documents
    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2007-322901    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2007-034251